This invention relates to compositions and a process for curing concrete, and more particularly to the use of curing compositions comprising natural resins.
The setting and hardening of concrete, also known as curing, requires, among other things, the presence of a proper amount of water to effect the hydration of the cement in the concrete mix. If an excessive amount of water evaporates from the mix during the curing process, then the concrete will not achieve its necessary or desired strength and the concrete article may shrink, causing cracks to form. Frequently, in order to prevent or to retard the evaporation of water during the early hardening period and to permit the proper hydration of the cement and curing of the concrete, curing compounds, such as liquid, membrane-forming materials, are applied to the surface of freshly-poured concrete. The curing compound is then allowed to remain on the surface of the concrete until the completion of the curing process, which is normally about one to four weeks from the time the concrete is placed.
Compositions comprising synthetic or natural resinous materials dissolved in solvents have been used as waterproofing agents and as curing compositions. These solutions are applied to freshly-poured concrete surfaces, and the solvents are allowed to evaporate to leave substantially resinous coatings which act to retard the evaporation of water from the concrete. Many of these compositions, particularly those which are intended as waterproofing agents, remain on the concrete surface indefinitely, to prevent the passage of water in either direction through the surface.
At times, it may not be desirable to have such coatings remain on the concrete surfaces after the completion of the curing period. For example, the residual coating material may interfere with the application of other materials to the concrete surfaces, such as floor tile, where the residual curing compound can inhibit the bonding of the tile adhesive to the concrete, or surface sealers, e.g., linseed oil, which might be applied to a surface because it will be subjected to excessive de-icing salt applications. These types of problems can impose significant limitations on the use of curing or waterproofing compounds specifically designed for their ability to remain on concrete surfaces indefinitely.
Another troublesome feature of prior art curing compounds is that many of the organic solvents which have been used in such compounds have been found to contribute to air pollution, and their use has been curtailed or banned in many jurisdictions. This is a particular problem because many of the previously used resins are only soluble in aromatic solvents, such as those containing high levels of benzene or toluene, and such solvents have been subject both to air pollution and occupational safety restrictions.
There are many such regulations restricting the use of these solvents, but one which is particularly well known and used as a model in many jurisdictions is "Rule 66" enacted by the City of Los Angeles, California to reduce the emission of photochemically reactive volatile liquids into the atmosphere. Although this rule is of course subject to legislative change, for purposes of this specification and whenever referred to hereinafter, the definition of liquids and solvents which violate Rule 66 is:
"1. Any liquid, including water, which contains more than a 20 volume percent aggregate total of:
a. All olefinic or cycloolefinic compounds, and PA1 b. All substituted aromatic hydrocarbons, and PA1 c. The branch chain ketones, and trichloroethylene PA1 a. 5 volume percent total blends of olefinic or cycloolefinic compounds, or PA1 b. 8 volume percent of blends of aromatic hydrocarbons (except toluene and ethyl benzene), or PA1 c. 20 volume percent total of blends of toluene, ethyl benzene, branch chain ketones, and trichloroethylene"
2. Any liquid, including water, which contains more than the indicated percentage concentrations of combinations of the following groups of solvents:
There are commercially available solvents specifically formulated to meet the requirements of Los Angeles Rule 66, but these have generally been found not to be suitable as solvents for the resins previously used in curing compounds. Thus, such curing compounds may not be able to be used in jurisdictions which have regulations corresponding to Rule 66.
Other less desirable features found in many of the previously employed curing compounds relate to the resin which is used. Many resins tend to turn yellow or darken on exposure to sunlight, making them unsuitable for coating certain outdoor work, such as light-colored building exteriors or other colored surfaces. Synthetic resins, which are generally petroleum derivatives, have become more and more expensive and difficult to obtain due to the world crude oil situation. Many natural resins require costly processing to remove undesirable materials or to modify their chemical composition before they are suitable for use as curing agents. Furthermore, some natural resins are far more scarce and expensive then others.